1. Field of the Invention
The invention relates to optical recording-reading systems using as information carrier an optically recordable and readable disk, information being recorded in the form of a disturbance of a radiation sensitive layer, for example a heat sensitive layer.
2. Description of the Prior Art
In these systems, the optical radiation is shaped by an assembly called optical head which may comprise: a GaAs semi-conductor laser, a collimating lens, a polarization separator assembly, a quarter-wave plate, a pivoting reflecting mirror, a lens for focusing on the disk, an assembly of servomotors for focusing on the disk and for tracking and photodetection cells for identifying the information read from the prerecorded disk or after storage of information.
The light beam emitted by the laser source after reflection from the reflecting mirror is focused by the focusing lens and supplies a luminous spot on a track of the information carrier. The reflecting mirror pivots about a pivot so as to allow movement of the spot transversely with respect to the track. It is then possible to ensure that the spot follows the track.
However, setting the mirror in an optimum position for supplying a reflected beam in a given direction requires great accuracy in the manufacture of the mirror pivot.
Furthermore, the recording-reading devices for disks may have their optical head mounted either on a head supporting device moving in translation along the radius of the disk, controlled by a motor, or at the end of an arm whose pivotoing center is outside the surface of the turntable driving the disk.
It is advantageous for the head to have an elongated form and to be disposed, depending on the case, along the translating or traversing device or in the extension of the arm. In one case, the large dimension of the optical head is then disposed transversely with respect to the track and in the other case it is aligned. Radial tracking by the spot with the help of the pivoting member poses then a problem for using the seam head in both head support configurations.